The moths are coming, and eating our trees

Oregon white oaks in some parts of the mid-Willamette Valley are being defoliated, along with some Douglas firs and ornamental plants.

The culprit, according to the Oregon Department of Forestry: an outbreak of western oak looper, a moth native to the Willamette Valley.

Affected trees show a scorched appearance, and, on closer inspection, the presence of large numbers of small caterpillars, about an inch long.

Population outbreaks of the moth also occurred from 1960 to 1964, 1977 to 1978 and 1992 to 1994.

Oregon white oaks appear to have suvived past outbreaks, but Douglas firs are less resilient, says Rob Flowers, entomologist for the forestry department. Firs can experience loss of growth, dead branches and tops, or even mortality if the defoliation occurs with dark beetle activity or during prolonged drought.

The best way to address an infestation is with a high-pressure spray, not with chemical treatments.